1. Field of the Invention
The present invention relates to an organic electroluminescence (hereinafter, abbreviated to “EL”) device panel.
2. Description of the Related Art
In recent years, an organic EL device which functions as a self-luminous device has been attracting attention for use in a flat panel display. The organic EL device generally has a sandwich structure in which an organic light emitting layer is sandwiched between two electrodes on a glass substrate. To allow light emitted from the organic light emitting layer to be extracted to an outside of the device, a transparent electrode is used as one of the electrodes, generally, an indium tin oxide (ITO) transparent electrode is used as an anode. Further, while an outer circumferential surface of the organic EL device is sealed with a sealing material, a current is caused to flow therein by an external driving circuit to thereby emit light.
The organic EL device that emits light by the principle as described above is used for a display of an in-vehicle audio system, a cellular phone, or the like, or as a display device thereof, since the organic EL device is excellent in visibility and flexibility and can emit light of various colors.
Incidentally, display pixels of the organic EL device panel having those characteristics are driven by a current. In addition, the organic EL device panel has a current dependent characteristic in which a light emission brightness of a pixel varies substantially proportional to a driving current. In particular, in an active drive type organic EL device panel, heat is generated locally at a time of driving. For example, in a case where the number of pixels of the panel is 320×240 pixels, when a current for one pixel is 750 nA, the current can be expressed by 750 nA×3×320×240=173 mA, which means that the current of about 173 mA flows through a single lead-out wiring. A contact resistance portion is provided between the lead-out wiring and a power source wiring, and heat is generated locally to increase a temperature of the lead-out wiring through which the current flows in a concentrated manner, in particular, a temperature of the contact resistance portion between the lead-out wiring and the power source wiring. Accordingly, there has been a problem of deterioration such as shortening of a lifetime of pixels of the organic EL device in the vicinity of the high-temperature portion, or generation and increase of a non-light emitting portion.
On the other hand, the lead-out wiring of a liquid crystal display (hereinafter, abbreviated to “LCD”) necessitates connections of a narrow pitch for realizing a display of high fineness. The narrow pitch connection can be realized by using solder or an anisotropic conductive film (hereinafter, abbreviated to “ACF”). In order to cope with the narrow pitch of several hundred μm or less, the connection with an FPC or a TCP corresponding to a plurality of lead-out wirings is preferably made through heat press bonding by using the ACF. The ACF is generally used for mounting the TCP on a liquid crystal display cell.
However, in order to realize a display having high fineness using the organic EL device, when heat press bonding is performed to establish an electrical connection of the lead-out wiring with the FPC as in the case of the LCD, there has been a problem in that image quality of the organic EL device is deteriorated due to heat transfer at the time of performing the press bonding. This is because the organic EL device is sensitive to heat and device characteristics are deteriorated, that is, light emitting efficiency is decreased or the lifetime thereof is shortened, due to the deterioration of the organic light emitting layer accompanying the heating. Thus, the heat press bonding for the connection of the lead-out wiring has been performed in a state where the lead-out wiring and an organic EL device portion are apart from each other to an extent that the deterioration is not generated so that the organic light emitting layer does not become equal to or higher than the temperature at which the deterioration is generated. However, with this method, an interval between a press bonding portion of the lead-out wiring and the organic EL device portion becomes large, so an outline of the organic EL device panel is increased, leading to a hindrance of miniaturization of the frame thereof.
In view of this, Japanese Patent Application Laid-Open No. H11-204256 proposes a method of manufacturing an organic EL device panel, a frame of which can be made small without causing deterioration due to heat press bonding by subjecting the organic EL device to a cooling process at a time of performing the heat press bonding using an ACF so as not to increase a temperature of the organic EL device.
The method of manufacturing an organic EL device panel disclosed in Japanese Patent Application Laid-Open No. H11-204256 involves only the cooling process at the time of manufacturing the panel. Therefore, a problem concerning deterioration due to heat at the time of driving after the panel is formed has not yet been solved. In short, the problem of the conventional organic EL device panel at the time of driving the organic EL device panel still remains. Accordingly, a temperature of the contact resistance portion between the lead-out wiring and the power source wiring becomes high due to the locally generated heat. As a result, deterioration such as shortening of a lifetime of pixels of the organic EL device in the vicinity of the high-temperature portion or generation and increase of the non-light emitting portion cannot be avoided. As a countermeasure, the deterioration due to heat generated at the time of driving can be reduced by increasing the number of the lead-out wiring or by thickening the wiring. However, there is a problem in that the increase in number of the lead-out wiring or the thickening of the wiring may hinder the narrowing of the pitch of the lead-out wiring or the miniaturization of the frame of the organic EL device panel.